These routines insert the character ch before the charac-
ter under the cursor. All characters to the right of the
cursor are moved one space to the right, with the possi-
bility of the rightmost character on the line being lost.
The insertion operation does not change the cursor posi-
tion.

All routines that return an integer return ERR upon fail-
ure and OK (SVr4 specifies only "an integer value other
than ERR") upon successful completion, unless otherwise
noted in the preceding routine descriptions.
Functions with a "mv" prefix first perform a cursor move-
ment using wmove, and return an error if the position is
outside the window, or if the window pointer is null.